Method of making a work holder



Dec. 12, 1961 J. 1.. OTTERS 3,012,314

METHOD OF MAKING A WORK HOLDER Original Filed Feb. 26, 1954 5Sheets-Sheet 1 INVENTOR.

/3 5 L (Dr-NW5 fl m? M 3 am J. L. OTTERS METHOD OF MAKING A WORK HOLDERFiled Feb. 26, 1954 Dec. 12, 1961 5 Sheets-Sheet 2 Original Dec. 12,1961 J, OTTERS 3,012,314

METHOD OF MAKING A WORK HOLDER Original Filed Feb. 26, 1954 5Sheets-Sheet s (90 Li 4 FIG. 18 F|G.23

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INVENTOR.

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Dec. 12, 1961 J. L. OTTERS METHOD OF MAKING A WORK HOLDER 5 Sheets-Sheet4 Original Filed Feb. 26, 1954 Dec. 12, 1961 J. L. OTTERS 3,012,314

METHOD OF MAKING A WORK HOLDER Original Filed Feb. 26, 1954 5Sheets-Sheet 5 FIG. 30

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FIG. 31

INVENTOR. \{yfi/N 1. 0772125 fl c United States Patent vided and thisapplication Jan. 2, 1958, Ser. No. 7 06,838 6 Claims. (Cl. 29423) Thisinvention relates to a method of making work holders, and particularlyto holders which are adapted to be used for holding a work piece so thatit may be subjected to a machining operation.

Work holders of this character are used for example in the chuck of aturning machine such as a lathe or drill press, milling machine, grinderor the like. The holder may also be used in a clamp of any kind which issuitable for holding a work-piece in position to permit operations to bemade upon it. The invention is particularly suited for holdingworkpieces which have a curved or irregular surface.

Heretofore, various attempts have been made to accomplish a satisfactoryholder for a curved surface, but they are subject to objections anddisadvantages hereinafter enumerated. One such method has required themachining of it from a block of metal. In some instances the holdingblock is made prior to the formation of the work-piece in production,wherefore it is necessary to make the holder by working from drawings ofthe workpiece. To do this, it is necessary to design the holder workingfrom the dimensions on the print or to calculate them from a knownreference point. Thereafter, the holder is either machined to correspondto the design, or is made of cast metal. A disadvantage of the latterproposal is that it is necessary first to make a pattern from thedrawing and then to make a mold and cast the metal. These stepsintroduce error to such an extent that the finished surface of thework-piece may not correspond precisely to the dimensions of the print.The resulting accumulation of error necessitates considerable time torework and to fit the work-piece to the holding block. Additionally, forsome irregular pieces, considerable time is required to design theholder and frequently the machined surfaces of the holding block do notconform exactly to the shape of the work-piece, thus re sulting inobjectionable point or line contact instead of area contact between thework-piece and holder. Moreover, the work-piece is frequently marred atthe points of contact.

A second method of making a holding block has embodied the machining ofthe block in a duplicating machine. This is usually performed in amilling machine which is equipped with a duplicating attachment. Usual-1y a master die is first made and is used for directing the path of afollower which in turn controls the movement of the cutting tool. Theobjection to this method is that if a large radius cutter is used thedetail of the master impression is poorly copied, while on the otherhand, if a small radius cutter is used, then many passes are required toduplicate the detail of the master die impression. Additionally, theaccuracy of duplication is subject to error in the transfer of motionfrom the follower to the milling machine table.

A third method of making a holding block embodies the casting of it in ametal mold. This is usually accomplished by splitting the work-piece andthen mounting the split section upon a plate. The plate is then insertedinto a mold and molten metal is poured into it thus forming the block bya casting process around the surface of the Work-piece. An objection tothis method, however, is the fact that the metal used is softer than thework-piece and that the life of the holding block is greatly shortened.Moreover, due to the softness of the metal, variations in the shapes andsize of the workice piece-resulting from the slight variations incidentto production-cause the impression in the holding block to become largerthereby decreasing the clamping ability of the holding block.

An object of the present invention is to provide a method of making awork holder which will overcome all of the foregoing objections andwhich will possess certain advantages, as follows:

(1) The engagement between the work-piece and the holder will beeffected at a number of preselected areas of contact which conformprecisely to the shape of the workpiece at such areas.

(2) The holding block will have a work-engaging face of relatively highstrength material which is attached to a back-up block of a softer orlighter material. The use of a lighter construction reduces the momentumof a rotating head resulting in the accomplishment of a higher cuttingspeed.

(3) The liner or facing sheet of the holder is fastened by a resilientbonding material to the backup block thus reducing vibration or chatterof the work-piece and resulting in the attainment of a smoother surfaceby the cutting tool during the machining operation.

(4) The method eliminates the necessity for hand fitting and results inuniform distribution of pressure between the holder and the work-piece.

Briefly, the foregoing objects are accomplished either by a stamping orforging operation. In the stamping operation a thin sheet of highstrength metal is formed around the Work-piece to be held; This may beaccomplished by cutting one specimen of the work-piece in half andforming the thin sheet around it. Thereafter, openings are made in thesheet at preselected areas and, thereupon, the sheet is placed over thehalf-section and mounted upon a flat plate. This assembly is then usedfor the formation of a second sheet which conforms to the contour of thefirst sheet, and which has portions of it entering the openings formedin the first sheet. The second sheet thus has bosses projectingtherefrom at spaced areas corresponding to the location of the openingspreviously formed in the first sheet. The second sheet is then attachedto a back-up block, as by a cementitious material, which includes aresilient bonding material, thereby resulting in the finished holderwhich when placed in the chuck of a turning machine with another holdersuitably formed to conform to the opposite side of the work-pieceoperates to securely grip it uniformly and securely.

The second method of making the work holder in accordance with thepresent invention embodies the formation of a first plate as aforesaidin conformation to the shape of the work-piece, and then formation ofsuitable openings at preselected locations, as aforesaid, and thereuponthe sheet and half section are rigidly fastened to a flat plate as bygrazing or soldering. The assembled unit is then placed in one head of apress, the opposite head of which carries a block of high strengthmaterial which is heated to a forging temperature and then the heads arebrought together, thereby forming a die cavity in the heated block.Afterwards, the block so formed is suitably heat-treated and constitutesthe workengaging holder which can be suitably fastened in a chuck orother clamping device.

This application is a division of application Serial No. 412,761, filedFebruarv26. 1954. now abandoned.

Referring now to the drawings,

FIG. 1 is a top plan View of a work-piece which is intended to'be heldby a work holder embodying the present invention;

FIG. 2 is a front elevation of the Work-piece;

FIG. 3 is a side elevation as viewed from the right of FIG. 1 (theWork-piece being symmetrical);

' FIGS. 18 to 22 inclusive;

FIG. 4 is a rear elevation of the work-piece;

FIG. 5 is a perspective view of the work-piece;

FIG. 6 is a perspective view of a half-section of the work-piece cut ona plane indicated by the line 66 in FIG. 5;

FIG. 7 is a perspective viewrof a plate which is shaped to conform tothe surface of the half-section shown in FIG. 6.

FIG; 8 is a perspective view of a flat plate which is used to completean assembly;

FIG. 9 is a perspective view showing the assembly of section, sheet andplate of FIG. 6 to 8 inclusive;

' FIG. '10 is a perspectiveview, partly broken away, showing theformation of a second plate over the assembly of FIG. 9; t

FIG. 11 is an enlargement of a portion of the assembly of- FIG. andillustrating the manner in which the second sheet is formed over theassembly of FIG. 9;

FIG. 12 is a perspective view of the second plate illustrated in FIG. 10but removed from the assembly'and inverted with respect to the positionshown in FIG; 10; FIG. 13 is a perspective view of a back-up block whichis used with the sheet of FIG; 12;

FIG. 14' is a perspective view showing an assembly of the sheet 12 tothe back-up block of FIG; 13;

7 FIG. IS'isan enlargement of a portion of the assembly of FIG. 14; f

FIG. 16 is a perspective viewof a chuck having work holders embodyingthe presentinvention attached thereto and utilized for holding thework-piece'illustrated in FIG. 5; i V

FIG; 17 is an enlargement showing a portion of the.

. piece;

FIG. 19 is a side elevation taken from the left hand side of FIG. 18; a

FIG. 20 is a front elevation of the work-piece of FIG. 18; 7

FIG. 21 is an elevation of FIG. 18; I

FIG. 22 is an elevation taken from the rear. of FIG. 18; FIG. 23 is aperspective view of the work-piece of taken from the right-hand sideFIG/24 is a perspective view of an assembly embodying a sheet which isformed around a half section of the work-piece shown in FIG. 23 inaccordance with the method illustrated in FIGS. 1 to 9 inclusive;

FIG. 25 is a section taken through a block'which is formed by theassembly of FIG. 24 and taken particularly on a plane indicated by theline 2525 of FIG. 24;

'FIG. 26 is a sectional detail enlargement of a portion of the assemblyof FIG. 25; p

FIG. 27 is a perspective view of the forged block (constituting theupper block of FIG. 25);

FIG. 28 is'a front elevationof a chuck having holdbolting, and thereupona sheet is formed'by a pressure operation around the top surface of thehalf section 11. This may be accomplished for example in the pressillustrated in FIG. 29 which has a lower press head and an upper presshead 21 arranged to be moved toward and from each other by means of ahydraulic ram 22. Thus, for example, the lower head which is movablewith respect to the press frame has an extension 26, the interior ofwhich is shaped to receive the plate 13 with the half-section 11 mountedthereon. Thereupon a blank sheet 15 may be'placed over the part 11 andthen a block 27 of material, such as lead, may be placed above the sheet15,. Then, as the ram 22 is operated to move the assembly against thehead 21, the sheet '15 is shaped to conform to the formation of the part'11. After the sheet 15 is removed from the press, openings 30 areformed therein at spaced pro-selected areas where it is desired to makecontact between the Work-piece and the work holder.

The next step in the method isthe formation of a second sheet 31 overthe sheet 15 by using the press illustrated in FIG. 29 in which case theblank for the sheet 31 is placed within the press above the assembly ofplate13, half-section 11 and sheet 15, the latter'having the openings 30cut therein. Upon operation of the press, the sheet 31 partakes of theformation of the sheet 15 with portions of the sheet 31 entering theopenings 30 to form bosses '32. This' is best illustrated in-FIG; 12where the sheet is removed'from thejpress and shown in invertedposition.

After the formationof the sheet 31 as aforesaid, the entire assembly ofFIG. 10 is placed within a mold shown in FIG; 31 and molten metal ispoured therein so as to form the back-up block 35 which is illustratedin FIG. 13. Thus, the block has bosses 36.Which correspond to the bosses3 2 in'the sheet31 and which interfit therewith whenever the sheet isplaced within the back-up block. In practice, the sheet31 is cemented tothe block 35 by means of an adhesive 37 which includes a resilientmaterial, such'as a rubberzcompound, thus providing a slight resiliencywhenever clamping action is exerted against the assembly of FIG; 14after'it has been placed ing blocks similar to that illustrated in FIG.27 attached 7 and FIG. 31 is a vertical section through a mold flaskwhich is used for forming the back-up block of FIG. 13.

Referring first to the formation of a holder which is made by thestamping process, and using for illustration the work-piecelfl shown inFIGS. 1 to 5 inclusive, the

- first step in the method comprises the severing of the work-piece intoa half section designated 11 in FIG." 6,

.this being cuton a plane indicated by the line 66 in FIG. 5. Thehalf-section so formed is then fastened to a plate 13 by any suitablemethod, such as soldering, or

in a .clamp holder. An adhesive suitable for this purpose is one which.is presently being sold by the B. F. Goodrich Company under thetrademark Plastilok. Preferably the bonding material forms a thin layerover the entire inter-fitting surfaces of the sheet 31 and block 35.

In FIG. 16, I have shown'a chuck 40. ashaving a pair of holding blocksassembled as in FIG. 14 and indicated at 41 and 42 respectively as beingclamped to'the chuck by means of adaptors 43 and 44 respectively.Inasmuch as the work-piece of FIG. 5 is symmetrical, it is onlynecessary to make a second holder corresponding to the holder .41 and touse them in opposing relationship to clamp the workpiece 10. i 7

FIG. 11, illustrates the manner in which tlle'bOSses 32 on the sheet 31are formed to enter the openings 30 in the sheet 15 while FIG. 17 showsthe manner in which the bosses 32 engage the surface 9 of the work-piece10, from which it may be seen that contact is effected between each boss32 and the work-piece'upon an area which is exactly complementary to thesurface of the workpiece.

A modification of my invention is illustrated in FIGS. 18 to 28 whereinthe forging process may be used for forming the clamping surface of thework holder,'and in these illustrations, I have shown a work-pieceindicated in general at 60 which again is a symmetrical piece. To carryout this process a half-section 62 is out along the plane indicated bythe line til-61 in FIG. 23 and is fastened, as by welding, or brazing,to a plate 65. Thereupon, a sheet 66 formed in the. same manner .as thesheet 15, as aforesaid, is placed over the half-section 62 and fastenedthereto as by brazing. The assembly of FIG. 24

may then be fastened to the head 70 of a press shown in FIG. 30, while ablock 71 of heated metal may be placed within an extension 72 of thelower press head 73. Upon operation of the press the top surface of theblock 71 has formed therein a cavity which is complementary to theformation of the sheet 66.

The block 71 may then be suitably heat treated to harden the workingsurface, and the block then constitutes the work holder. One such holderis shown for example in perspective view in FIG. 27, and inasmuch as thework-piece 60 is symmetrical, it is only necessary to make another blockcorresponding to the shape of that designated 71 and then to mount themwithin a suitable chuck 75, as shown in FIG. 28. In this form of holderthe contact areas between the holder and the work-piece are indicated at80 to 84 respectively. These are preselected areas which serve toeffectively grip the workpiece and hold it against movement with respectto the holder.

A method of making a work holder made in accordance with the presentinvention is advantageous in that a greater degree of accuracy can beobtained without the accumulation of error experienced in the formationof previous work holders while at the same time a hardened work surfaceis obtainable at a relatively low cost. The invention eliminates thenecessity for making designs and patterns and reduces the manufacturingoperation to a minimum. In addition, the invention is well suited forthe formation of a Work holder which corresponds to any configuration ofWork-piece which can be cast.

I claim:

1. A method of making a work holder comprising pressing a blank of sheetmaterial into engagement with a portion of a work-piece to be held,until the sheet is complementary to the contour of said portion,removing the sheet from the work-piece, forming holes at preselectedspaced locations in the sheet while it is separated from the work-piece,placing the sheet into reengagement with the work-piece, pressing asecond member into engagement with the surface of said sheet while it isasesrnbled onto the work-piece until said member is complementary to thecontour of the sheet, causing portions of said member to enter therespective holes in the sheet and to engage the underlying surface ofthe workpiece, thereby forming bosses which are complementary to thecontour of the Work-piece and which are defined by the pre-selectedareas of said holes and then separating the second member from theassembly consisting of the work-piece and said sheet.

2. A method of making a work holder according to claim 1 wherein thesecond member comprises a sheet of material and wherein a back-up blockis affixed thereto after the second sheet has been separated from theassembly of the work-piece and the first sheet.

3. A method of making a work holder according to claim 1 wherein thesecond member comprises a heated metallic block.

4. A method of making a Work holder according to claim 2 wherein theback-up block is molded onto the sheet by a casting operation while thesecond sheet is positioned on the assembly of the work-piece and thefirst sheet.

5. A method of making a work holder according to claim 1 wherein thesecond member is a block of metal into which a cavity is formed by aforging operation, using the assembly of the Work-piece and the sheet asa punch, after which the block when separated from the assembly ishardened on the work engaging surface thereof.

6. A method of making a work holder according to claim 1 wherein thework-piece comprises a half-section of the work-piece to be held, andwherein the half-section is mounted upon a supporting plate with theplane surface of the section in contact with the plate therebypresenting to said sheet the contoured surface of the work-piece towhich the sheet is to be made complementary.

References Cited in the file of this patent FOREIGN PATENTS 705,856Germany May 12, 1941

